Heretofore, there has been a constant need in the fields of disinfection and sterilization to have indicators present during the sterilization or disinfection of medical devices to demonstrate that processed articles have been exposed to the active ingredient of the disinfectant or sterilant. There are several types of indicators used in the field, each providing various levels of assurance to the user that the appropriate processing requirements were met.
The first type of indicator is a process indicator. A process indicator provides an indication to the user that the articles were processed, but not whether or not the appropriate conditions for sterilization or disinfection were achieved during the processing cycle. Commonly, process indicators are colorimetric in nature and appear on the labeling of self-contained biological indicators (SCBI) or on autoclave tape. The color change of this type of indicator is almost instantaneous.
A second type of indicator is a chemical indicator (CI). A chemical indicator is able to detect semi-quantifiable to quantifiable amounts of the active used in the sterilization or disinfection process. The use of a chemical indicator with various articles provides a high level of assurance that the required active concentration was achieved. Chemical indicators are commonly placed with articles to demonstrate that the active ingredient was able to completely penetrate the processed articles. For instance, CIs may be placed within a wrapped pack that is being steam sterilized.
Chemical integrators are yet another type of indicator. Integrators will measure more than one parameter. For instance, an integrator will not only indicate that the appropriate concentration of active was achieved but that the active remained at the concentration for the minimum time required. Another common variable that may be measured by integrators is the temperature of the system.
The final type of indicator is the biological indicator (BI). Biological indicators provide a high degree of assurance that sterilization conditions were met within the processor or processed articles. This type of indicator is meant to represent the worst case for the processing system by providing an extremely high number of highly resistant organisms to that particular process within or on the indicator. Usually spores are the organism of choice for sterilization systems.
Currently, many process and chemical indicators for oxidative high level disinfection systems and sterilization processes, such as liquid peracetic acid (PAA) and hydrogen peroxide (H2O2), rely on an oxidative bleaching-type reaction resulting in a gradual decrease in the color intensity with exposure time and/or active concentration. Indicators that do not rely on an oxidative bleaching reaction may change color with PAA or H2O2 in the presence of either a halogen source or a transition metal salt.
A commercial chemical indicator (i.e. STERIS System 1 Chemical Indicator) contains a dye that exhibits a vivid purple color before exposure to liquid peracetic acid, and after exposure to appropriate levels of peracetic acid, the indicator is a light pale gray color. The color change result is due the indicator dye being oxidatively bleached by the peracetic acid during the processing cycle. Another commercial indicator is magenta and upon exposure to the oxidative capacity of peracetic acid changes to peach. The peach color results from an underlying dye that is not susceptible to oxidation.
The 3M Comply 1249 Liquid Peracetic Acid Chemical Indicator requires a halide salt (alkaline earth metal halide or alkali metal halide salt) to obtain the color change in the dye when exposed to peracetic acid vapors. The vapor from the peracetic acid penetrates through the vapor permeable backing of the chemical indicator blister pack and oxidizes the halide salt to release the halogen. The halogen then reacts with the indicator dye (in the sodium salt form) to change the color.
Other chemical indicators for vaporous hydrogen peroxide sterilization processes rely on the oxidative nature of the H2O2 either directly or indirectly. For instance, a chemical indicator for vaporous hydrogen peroxide systems can contain metal salt in addition to at least one indicator dye. The H2O2 reacts with the metal salt which in turn reacts with dye to get a distinct color change.
While the above indicators and methods are generally effective, they may be complex to manufacture and expensive to use. They also rely on interactions with a halide salt or by other direct means to achieve a desired color change.